In recent years, enzyme reactions have been actively utilized on a commercial scale in the phamaceutical and food industries. Since enzymes are expensive and when used in the form of a solution, are difficult to separate or recover from the product after reaction, techniques of immobilizing an enzyme on a support material to provide a so-called immobilized enzyme have been extensively studied.
Investigations have been made on the utilization of a membrane such as an ultrafiltration membrane in order to provide a method which enables the separation of the reaction product from the enzyme to be effected simultaneously with the enzyme reaction. Such a method has attracted attention because it makes possible very easily to conduct coarse separation treatment by molecular weight cut-off as a pretreatment of fine separation and purification.
One typical example proposed so far is a membrane reactor on which an enzyme is immobilized. Specifically, a method which comprises enclosing an enzyme into a porous portion of an anisotropic ultrafiltration membrane and coating the porous portion (Japanese Patent Application (OPI) No. 25686/84), and a method which comprises enclosing and entrapping an enzyme together with a gel in the porous portion (Japanese Patent Publication No. 41238/82) are disclosed. None of these methods, however, can retain the enzyme stably. Thus, no membrane has been developed on which an enzyme can be retained and immobilized stably.